1. Field of the Invention
The present invention relates to a pump system provided with a hydraulic pump body and a PTO unit, and an axle-driving system which is provided for each drive axle and independently drives the corresponding drive axle in cooperation with an actuator.
2. Background Art
There has been conventionally used in various fields a pump system which includes a hydraulic pump body and a PTO unit and has a structure that an input from a driving source is input to both of the hydraulic pump body and the PTO unit (see, for example, JP-A 2003-291674).
Such a pump system is particularly useful in a working vehicle or the like, for example, because the hydraulic pump body can form a travel transmission path in cooperation with an actuator such as a hydraulic motor body or the like arranged apart from the pump system, and the PTO unit can form a PTO transmission path for transmitting a power to an external working machine.
However, the conventional pump system does not sufficiently take cooling efficiency for a PTO clutch mechanism in the PTO unit into consideration.
In other words, the PTO unit has a PTO shaft, and a PTO clutch mechanism which selectively engages/disengages a power transmission from the driving source to the PTO shaft.
Specifically, the PTO clutch mechanism is accommodated in a housing of the pump system which can reserve oil. The reserved oil within the housing can somewhat cool the PTO clutch mechanism. However, in the case that the reserved oil is retained, it is impossible to expect a sufficient cooling effect.
An aspect of the present invention has been made in view of the conventional art, and a main object of the present invention is to provide a pump system in which a hydraulic pump body and a PTO clutch mechanism are accommodated in a housing which can reserve oil, and which can improve a cooling efficiency for the PTO clutch mechanism.
In addition, there is a known axle-driving system which includes a motor unit forming a non-stepwise speed change device in cooperation with the actuator. The axle-driving system is provided for each drive axle.
The known axle-driving system will be described by taking a case in which a hydraulic pump unit is used as the actuator and a hydraulic motor unit in fluid communication with the hydraulic pump unit is used as the motor unit (e.g., U. S. Pat. No. 4,920,733 or Japanese Utility Model Publication No. S 56-77437).
In the axle-driving systems described in these prior art documents, a turning ability of the vehicles, especially an ability to make a small turn of a vehicle can be advantageously improved since each of the drive axles can be independently driven with changing its rotational speed. The miniaturization of the entire apparatus, however, has been left to be improved.
Particularly, to make a smaller turn of a vehicle, it is preferred to provide with a brake unit for each drive axle. Neither of the prior art documents, however, mentions such a brake unit, and, of course, there is no description as to how the brake unit could be reduced in its capacity and size.